A number of proposals have heretofore been made on catalysts used in gas-phase catalytic oxidation of propylene to produce acrolein and acrylic acid, or on catalysts used in gas-phase catalytic oxidation of isobutylene, TBA or MTBE to produce methacrolein and methacrylic acid. Many proposals have been made as well on processes for producing such catalysts.
In, for example, JP-A-98143/1983, JP-A-109946/1991, etc. are reported processes which comprise adding, at the time of preparation of a catalyst precursor, an organic compound such as aniline, methylamine, pentaerythritol or the like in order to obtain a catalyst of controlled pore size. Also in JP-A-315147/1988, JP-A-4048/1992, etc. are reported processes which comprise adding a starch. These proposals have an advantage-that by applying a heat treatment, the organic compound added is removed and, by varying the size of the organic compound used, the pore diameters of the catalyst obtained can be controlled freely.
In the catalysts produced according to the processes described in the above literature, however, it may appear, when the pore diameters of catalyst are made larger for improved catalyst performance, that the molded catalyst has a low strength and, at its packing stage, gives rise to powdering and disintegration owing to the mechanical impact applied during the packing. When the powdering and disintegration appear at a striking proportion, a decrease in substantial packing volume of catalyst and/or an increase in pressure loss takes place and, resultantly, it may not be possible to carry out an intended reaction under predetermined conditions.
In general, when a molded catalyst of low strength is packed into a tubular reactor, there is employed, in many cases, a packing method wherein a countermeasure for preventing the powdering and disintegration of such a solid catalyst has been taken.
In, for example, JP-A-31351/1993 is disclosed a method of, in packing a solid catalyst into the tubular reactors inside a fixed bed reactor, dropping the solid catalyst with a string-like substance being interposed. Also in JP-A-64902/1994 and JP-A-24232/1998 are disclosed a method of using a catalyst cartridge and a method of using a catalyst filling machine having an openable or closable catalyst outlet. Further in JP-A-42400/2000 is disclosed a method of using a cylindrical container which has an inner wall of such a hardness as to show no deformation when a particulate substance has been fed thereinto and which has, at the bottom, an opening having an opening and closing mechanism.
In reactors of multi-tubular type used industrially, however, there are several thousands or more of tubular reactors in some cases; therefore, it is very complicated to carry out the operations described in the above literature, for each of the individual tubular reactors, and the methods described therein are not realistic.
In order to avoid such inconveniences, there are methods of packing, into a tubular reactor, an additive-containing catalyst precursor having a sufficient strength during the packing, then passing a gas through the tubular reactor, and, in this state, applying a heat treatment to the additive-containing catalyst precursor to remove the additive in the catalyst precursor.
In, for example, JP-A-358542/1992 and JP-A-182933/1996 are disclosed a method of coating at least part of the surface of a catalyst precursor with an organic polymer compound, and a method of using an additive-containing catalyst precursor obtained by impregnating, into the pores of a catalyst precursor, an organic compound which is a solid at normal temperature and melts at 300° C. or below or which is soluble in organic solvents. Also in the Examples of JP-A-70719/2000 is described a method of packing, into a tubular reactor, a catalyst precursor containing carboxymethyl cellulose or methyl cellulose ether and calcining the catalyst precursor at 510° C. for 3 hours with air being passed.
The study by the present inventors, however, revealed that, with the conventional methods described in the above literature, etc., a reduction in catalyst performance takes place in some cases and a problem remains in reproducible production of catalyst.
Hence, it is desired to develop a method for packing an additive-containing catalyst precursor into a tubular reactor and then applying a heat treatment to the catalyst precursor, which method gives a small reduction in catalytic performance and is simple and highly reproducible when applied industrially.